If I understand you correctly. When you say you loose the background for the "whole control" I'm assuming you mean your tlw.
Since tlw is not defined in this function I'll assume its defined somewhere else in your file.
Or if your copying that example I posted in that thread, did you forget to create the tlw?
By what you said though my guess is that you created some tlw control elsewhere that has a custom backdrop and then your trying to dynamically create dropdowns and place them on that tlw.
If so your problem would probably be because when you create the backdrop its parent is tlw & you use SetAnchorFill() which fills up the entire space of its parent, which is the tlw and probably not what you wanted because it would overlap your tlw's custom backdrop. The default backdrop is probably sitting on top of your custom tlw backdrop hiding it.
Lua Code:
local bd = WINDOW_MANAGER:CreateControlFromVirtual("comboBox"..name, tlw, "ZO_DefaultBackdrop")
bd:SetAnchorFill()
Only going by what you said, it sounds like you don't need the backdrop at all, since the parent control has its own backdrop where the dropdowns will be placed.
If your just wanting to use the backdrop to outline a box/area around the dropdown then you should probably do something like:
Lua Code:
local comboName = "combo"..name
local comboBox = WINDOW_MANAGER:CreateControlFromVirtual(comboName , tlw, "ZO_ComboBox")
comboBox:SetDimensions(150, 30)
comboBox:ClearAnchors()
comboBox:SetAnchor(TOPLEFT, tlw, TOPLEFT, x, y)
-- make the backdrop parent the comboBox
local bd = WINDOW_MANAGER:CreateControlFromVirtual("comboBox"..name, comboName , "ZO_DefaultBackdrop")
-- Now using achorFill would make the backdrop the same size as the comboBox, although
-- that means it probably wouldn't show up because its not big enough, it will
-- be hidden behind the comboBox
-- bd:SetAnchorFill()
-- so add some padding and anchor it around the comboBox
bd:SetAnchor(TOPLEFT, comboBox, TOPLEFT, -10, -10)
bd:SetAnchor(BOTTOMRIGHT, comboBox, BOTTOMRIGHT, 10, 10)